function ReadCookie(CookieName)
{
  var CookieString = document.cookie;
  var CookieSet = CookieString.split (';');
  var SetSize = CookieSet.length;
  var ReturnValue = "";
  var CookiePieces;
  var x = 0;
  
  for (x = 0; ((x < SetSize) && (ReturnValue == "")); x++)
  {
    CookiePieces = CookieSet[x].split ('=');

    if (CookiePieces[0].substring (0,1) == ' ')
    {
      CookiePieces[0] = CookiePieces[0].substring (1, CookiePieces[0].length);
    }
    
    if (CookiePieces[0] == CookieName)
    {
      ReturnValue = CookiePieces[1];
    }
  }
 
  if (ReturnValue == 'yes') {
	document.location.href='ageok.html';
  }
  else if (ReturnValue == 'no') {
	window.location.replace('agenotok.html');
  }
}

function WriteCookie(CookieName,CookieValue)
{
    document.cookie = CookieName + "=" + escape(CookieValue);
	return CookieValue;
}

function fixDate(date) {
  var base = new Date(0);
  var skew = base.getTime();
  if (skew > 0) { date.setTime(date.getTime() - skew); }
}

// determine age
function howOld(day,month,year) {
    var c = new Date(); // a new instance
    fixDate(c);

    var thisDay = c.getDate();
    var thisMonth = c.getMonth() + 1;
    var thisYear = c.getFullYear();

    var yearsold = thisYear - year; 
    var monthsold = 0;
    var daysold = 0;
    var age = '';

    if (thisMonth >= month) {
      monthsold = thisMonth - month;
    }
    else {
      yearsold--;
      monthsold = thisMonth + 12 - month;
    }

    if (thisDay >= day) {
     daysold = thisDay - day;
    }
    else {
        if (monthsold > 0) {
          monthsold--;
        }
        else {
          yearsold--;
          monthsold += 11;
        }
        daysold = thisDay + 31 - day;
    }

    if (yearsold < 0) return '';

    if ((yearsold == 0) && (monthsold == 0) && (daysold == 0)) return '';

    if (yearsold > 0) {
        age = yearsold;
        if (yearsold > 1) age;
        age += ' ';
    }

    return age;
}


function doSubmit() {
 var f = document.form1;
 var dob,theMonth,theDay;

 /* Validate month: check for digits, then check:  1 <= month <= 12 */
 if(f.dob_month.value.match(/\d{1,2}/)) {
   theMonth = eval(f.dob_month.value);		
   if(!(theMonth <= 12 && theMonth >= 1)){
     alert('Please enter a valid month of birth.');
     f.dob_month.focus();
     f.dob_month.select(); 
     return(false); 
  }
 } 
 else {
  alert('Please enter a valid month of birth.');
  f.dob_month.focus();
  f.dob_month.select(); 
  return(false); 
 }
  
 /* Validate day: check for digits, then check:  1 <= day <= 31 */
 if(f.dob_day.value.match(/\d{1,2}/)) {
   theDay = eval(f.dob_day.value);
   if(!(theDay >= 1 && theDay <= 31)) {
      alert('Please enter a valid day of birth.'); 
      f.dob_day.focus(); 
      f.dob_day.select(); 
      return(false); 
   }
 }
 else {
   alert('Please enter a valid day of birth.'); 
   f.dob_day.focus(); 
   f.dob_day.select(); 
   return(false); 
 }

 if(!f.dob_year.value.match(/\d{4}/) || f.dob_year.value=="0000") { 
    alert('Please enter a valid year of birth (xxxx).'); 
    f.dob_year.focus(); 
    f.dob_year.select(); 
    return(false); 
 }
 
 var age = howOld(f.dob_day.value, f.dob_month.value, f.dob_year.value);
 
 if((age >= 21) && (age <= 150)) {
    dob = f.dob_year.value + "-" + f.dob_month.value + "-" + f.dob_day.value;
	WriteCookie('admit','yes');
	document.location.href='ageok.html';
 }
 else {
   WriteCookie('admit','no');
   window.location.replace('agenotok.html');
   return(false);
   }

//f.submit();
return(true);
}
<!-- This is not needed
function goPage() {
  if(doSubmit()) {
      document.location.href='index.htm';
  }
}
 -->